Author
|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/1/2004 Publication Date: 3/7/2005 Citation: Berry, E.D., Miller, D.N. 2005. Cattle feedlot soil moisture and manure content: II. Impact on Escherichia coli O157. Journal of Environmental Quality. 34:656-663. Interpretive Summary: Both the moisture and manure content of soils at cattle feedlot surfaces likely affect the ability of Escherichia coli O157 to grow and survive in these soils. We examined the effects of different moisture contents (10 to 60%) and manure levels (5, 25 and 75%) on populations of E. coli O157, generic E. coli, and coliform bacteria in feedlot soils. Generally, E. coli O157 numbers either survived or multiplied at all but the lowest moisture levels examined. At 25% and 75% manure contents, increases in manure content of the soils changed the effect of moisture on E. coli growth and survival, by increasing the volume of water needed to produce the same effect on the pathogen's growth or survival. E. coli and coliform populations responded similarly to those of E. coli O157. The effects of cycling moisture levels and different drying rates on naturally-occurring E. coli O157 in feedlot soils were also examined. Low initial levels of E. coli O157 were reduced to below countable levels by 21 days, but naturally-occurring generic E. coli populations persisted at levels greater than 300 viable cells per gram of soil for up to 133 days. We conclude that E. coli O157 can persist in feedlot soils over a wide range of water and manure contents and may even grow under certain conditions. Manure content changes the effect of moisture on E. coli growth in feedlot soils, most likely by reducing the availability of the existing water for cell growth. Further investigations will be necessary to determine if moisture and manure content can be manipulated to reduce the survival and transmission of this pathogen in cattle and the feedlot environment. Technical Abstract: The moisture and manure contents of soils at cattle feedlot surfaces vary spatiotemporally and likely are important factors in the persistence of Escherichia coli O157 in these soils. The impacts of different moisture contents (10 to 60%) and manure levels (5, 25, and 75%) on populations of E. coli O157:H7, generic E. coli, and coliforms in feedlot soils were evaluated. Generally, E. coli O157:H7 numbers either persisted or increased at all but the lowest moisture levels examined. Manure content modulated the effect of moisture on E. coli growth; for example, at 30% moisture and 25% manure, E. coli O157:H7 increased by 2 log CFU g'1 soil DM in 3 days, while at 30% moisture and 75% manure, initial populations remained stable over 14 days. E. coli and coliform populations responded similarly to those of E. coli O157:H7. The impact of cycling moisture levels and different drying rates on naturally-occurring E. coli O157 also was examined. Low initial levels of E. coli O157 were reduced to below enumerable levels by 21 days, but indigenous E. coli populations persisted at populations of >2.50 log10 CFU g'1 DM up to 133 days. We conclude that E. coli O157 can persist in feedlot soils over a wide range of water and manure contents and may even grow under certain conditions. Manure content modulates the effect of moisture on E. coli growth, presumably by affecting the water activity of the soils. Further investigations will be necessary to determine if these variables can be manipulated to reduce the survival and transmission of this pathogen in cattle and the feedlot environment. |
